glue a slab of 1" foam under the board that you will set the bear on--stick one to three skinny dowel through the board into the foam and slide the cake down onto that--be careful to not glue where you will place the dowel--glue around those areas--

sometimes i let the middle dowel extend though the top of the cake so i have a handle during delivery and for ease of movement while decorating too--then i clip it off after delivery and cover the hole--easier to hold onto in the car --stuff like that--

if you are driving solo--you can place the dowel up through a hole in the top of the box too so it stays as stationary as possible